Hello! I'm going to try and explain this the BEST I can.
In America today you rarely come upon somebody saying," Geez! That's hip/groovy!" without looking like an idiot. If you were to say," Geez! That's cool!" it would sound better today.
If you were to go back in time to any decade within the past 100 years, what would be an old saying that nobody would say today without looking stupid?
Sorry for my poor explanation. This is the best way I can type what I'm thinking.
Thanks for reading!

You know that big book "Imidas" that comes out with all the new terminology? Any Imidas from more than five years ago would have lotsa dead terms. In fact, I remember one publication that was a parody of Imidas (literally taken from "imi-dasu") called "Shigodas" that focussed on hopelessly "ungroovy" terms that one still might hear. Of course, Shigodas came out in like 1990, so it's more like Zombidas now.